The long-range objective of our laboratory is to understand the molecular basis of crown gall, a neoplastic disease of dicotyledonous plants. At present, it is known that tumor formation involves a stable transfer of genetic information, the Ti plasmid T-DNA, from Agrobacterium tumefaciens to the plant cells. Furthermore, the evidence suggests that the Ti plasmid sequences referred to as the "common DNA" have a central role in oncogenesis: all Ti plasmids have either a highly conserved or related version of the common DNA; these sequences are part of the T-DNA in all tumor lines examined; they are transcribed in the tumor tissues; and mutations introduced into this region of the Ti plasmid affect tumor formation. Clearly, a detailed knowledge of the transcription and possible translation products of the T-DNA, in particular the common DNA, should lead to a better understanding of the molecular basis of this tumorigenic process. Toward this end, we have determined the direction of transcription and approximately 80% of the nucleotide sequence of one of the common DNA "oncogenes." In addition, we have made gene fusions between this oncogene and the E. coli enzyme beta-galactosidase. We have raised antisera against the fused gene product and have determined that the antisera can react with the oncogene portion of the hybrid protein. We are currently using the antisera to detect the oncogene protein product in tumor tissues. The study of crown gall tumorigenesis is "health related"; it is concerned with the basic mechanisms of tumor formation. In addition, our studies should eventually contribute to an understanding of the roles of hormones in regulated cell growth (normal plant tissues require phytohormones for growth whereas crown gall tumor tissues are hormone independent) and of the mechanisms of eucaryotic gene expression (we should eventually learn what DNA sequences constitute effective promotors of transcription in plants). The study of crown gall has already revealed that procaryotes can induce cancer in eucaryotes and that genetic recombination between procaryotes and eucaryotes is a naturally occurring phenomenon. It is anticipated that the continued study of crown gall will yield additional insight into basic biological processes.